It is well known in the art to utilize PAR (parabolic aluminized reflector) lamps for general spot lighting applications. In particular, PAR 38 (those with a 4.75-inch face diameter) spot lamps have become exceptionally popular for short-to-medium-distance outdoor uses as well as indoors for display, decoration, accent, inspection, and downlighting applications. Examples of such spot lamps are manufactured and sold by the assignee of the instant invention under the product designations 75 PAR/SP, 150 PAR/SP, and 150 PAR/3SP. Typically, these lamps are of hardglass and include a medium skirt (screw-type) or side prong base at the rear thereof for connecting the lamp to the desired power source.
The beam produced by a PAR lamp is typically of substantially conical configuration and provides a substantially round pattern. This pattern changes to being oval or elliptical should the lamp be aimed at an acute angle with the light-receiving surface. These lamps also may possess a rated average life of from 2000 to 4000 hours (with many more recently introduced models exceeding this), operate readily from standard household current (120 volt) and produce a beam having an output typically ranging from about 700 to about 3300 lumens.
Prior spot lamps, such as those of the type PAR 38 variety, include, in an early version, a lens that has either a stippled or irregular lens surface typically obtained by shot or sand blasting. The stippled surface usually appears over substantially the total face of the lamp lens. The resultant light pattern from such a surface provides a generally undesired asymmetrical pattern which is essentially a function of the stipple density. Moreover, a further drawback of existing spot lamps of this type is that there is very little, if any, control of the beam pattern.
A presently existing spot lamp is also shown in the aforementioned copending application Ser. No. 380,495. As stated, the lens of this lamp has a series of concentrically disposed fluted rings on the interior surface of the lens, each ring having a progressively increased radius, in combination with an outer concentric ring portion adjacent to and wider than any one of the fluted rings. This outer concentric ring portion includes a stippled surface, also located on the interior of the lens. By combining fluted concentric rings having specified radii with different stipple densities, a more controllable, symmetrical, and pleasing (softer) spot beam pattern is realized, particularly when utilizing a standard cross-axis mounted incandescent filament (where the filament is substantially parallel to the lens). However, when the lens is used with an axially mounted filament (where the filament lies perpendicular to the lens), these lenses provide a "pinwheel" beam pattern which is undesirable in that it does not meet normal candlepower distribution criteria. Accordingly, the "pinwheel" beam pattern is generally deemed visually unacceptable as a spot beam pattern.